Brominated compounds are commonly included as additives in expandable polystyrene for the purpose of reducing the flammability of the product material. Numerous patents exist describing ways to integrated these additives into polystyrene beads used to mold shaped objects. The flame suppression involves both accelerated polymer shrinkage from an advancing flame front and the ability of liberated bromine atoms to quench the oxidative chemistry of the flame. Brominated flame retardants are extensively used in polystyrene products intended for use in building construction or packaging. On the other hand, these additives are prohibited in polystyrene products used as food or beverage containers. Consequently, the presence or absence of brominated compounds in polystyrene beads used by foundries for lost foam casting has depended, inadvertently, on whether the selected suppliers serves the construction/packaging or food/beverage industries.
Commercially available expanded polystyrene beads contain integrated bromocompounds (intended to serve as flame retardants) have been used for lost foam casting of aluminum. This has occurred primarily in Europe where beads containing hexabromocyclododecane (HBCD) (FIG. 1) or tetrabromocyclooctane (TBCO) (FIG. 2) have been produced by German chemical manufacturers. It has been discovered (by applicants) that commercially available expanded polymer containing integrated bromocompounds have produced significantly fewer fold defects in engine castings. However, expanded polystyrene beads with these integrated bromocompounds require an additional lubricant additive for use in lost foam castings. Polystyrene beads with the integrated bromocompounds are also expensive. Furthermore, these commercially available beads with integrated HCBD or TBCO can be environmentally undesirable because the bromine atom is located on the aromatic ring. Thus it would be desirable to provide a method of inexpensively producing environmentally acceptable expanded polystyrene beads for use in making mold shaped objects for lost foam aluminum casting.